This laboratory is evaluaitng the mechanisms of induction of thymic lymphoma in the AKR mouse. We have identified retroviruses with different host range and phenotypic properties. Some accelerate lymphoma after inoculation into neonatal AKR mice (LAc ion). These appear after 6 months of age. Others are not leukemia accelerating (LAc-) and are the products of AKv-l and Akv-2 genes. We propose to clone viruses from these two classes and study their genome by oligonucleotide mapping. Our source of LAc ion viruses are the SL viruses produced in the fluids of some of the continuous in vitro lines which were derived from the thymus of mice with AKR spontaneous lymphoma. This project proposes studies of the thymus of preleukemic animals to look at the specific age related changes in virus expression and cellular interaction which result in malignancy. This will be done using thymic epithelium, (primary explants) co-cultured with thymic lymphocytes. Virus expression in both epithelial cells and thymocytes will be evaluated.